JSFiddle - React, Tailwind, and code Playground

HTML

<table id ="tbl">
  <tr>
    <td>5</td>
    <td>12</td>
    <td>15</td>
    <td>17</td>
  </tr>
  <tr>
    <td>3</td>
    <td>6</td>
    <td>12</td>
    <td>13</td>
  </tr>
</table>
Results:
<div id="results"></div>

JavaScript

$(function() {
    var index = 0;
    $("#tbl tr").find("td:gt(0)").each(function() {
        $this = $(this);
        $("#results").append(++index + ": " + (parseInt($this.html(), 10) - parseInt($this.prev().html(), 10)) + "<br/>");
    }) 
});